This invention relates to telephone systems and the like communicating between a handset and a base station with infrared light energy and, more particularly, in a communications system wherein a photodetector receives light signals on an active sensing surface thereof and outputs an electrical signal proportional to the amount of light impinging on the active sensing surface, reflective concentrator apparatus for aiming the photodetector at a field of view and for improving the signal-to-noise ratio and providing signal gain comprising, a tubular reflective concentrator having an inlet end, an outlet end which is smaller than the inlet end, a focal plane located adjacent the outlet end, and a reflective inner surface disposed between the inlet end and the focal plane and reflecting substantially all light beams entering the inlet end onto the focal plane, the tubular IR reflective concentrator having the photodetector disposed adjacent the focal plane with the active sensing surface thereof disposed in the focal plane whereby light beams entering the inlet end are reflected onto the active sensing surface of the photodetector.
Communications systems containing a bi-directional or uni-directional link by means of infrared (IR) light energy are known in the art. There are also several examples of telephone systems of one kind or another employing IR linking. Examples of the foregoing can be seen with reference to the following U.S. Pat. Nos. Nash (1980): 4,241,236; Lucey (1984): 4,450,319; Baker et al. (1984): 4,456,793; Crimmins (1985): 4,553,267; Avakian (1988): 4,727,600; Parienti (1988): 4,776,000; Matheny (1989): 4,829,561; and Streck et al (1989): 4,856,046.
A typical prior art telephone system employing an IR link is shown in FIG. 1 (as exemplified by a portion of FIG. 3 in the Baker et al. patent referred to above). The base station 10 is located on the ceiling 12 and includes a bi-directional IR link 14. The user devices can comprise a desktop device 16 having its own bi-directional IR link 14' and attached handset 18 or a portable handset 18' having the bi-directional IR link 14' built in. A computer terminal with modem can also communicate with the base station 10 using the desktop device 16. The prior art teachings relative to the actual IR link in an IR telephone system, or the like, are either non-definitive boxes labelled "IR", or "IR LINK"; or, are as depicted in FIGS. 2 and 3. For example, the bi-directional IR link 14 of FIG. 2 has a light emitting diode 20 with a conical emission pattern of less than 90.degree. placed adjacent to a photodiode 22 having a similar conical field of view and response to incoming IR signals. FIG. 3 depicts an IR control signal transmitting device comprised of a plurality of light emitting diodes 20 with conical emission patterns of about 30.degree. placed along a semi-circular support to radiate in a semi-annular arc. A similar approach is employed in the above-referenced Avakian patent wherein a plurality of pairs of light emitting diodes 20 and photodiodes 22 are mounted on a pair of partial spherical surfaces on opposite ends of a fixed IR signal repeater system.
The foregoing prior art approached to a bi-directional IR link are probably suitable for the purpose in a fixed handset system where the IR link associated with the handset can be pointed in an optimal manner towards the IR link of the base station and remain there during use. In a truly portable IR-linked handset, however, the prior art approaches to the IR link (or their ignoring of the subject altogether) are totally unacceptable for a commercially-successful and user-acceptable system. In this regard, users of a portable, wireless telephone expect it to have certain operating characteristics regardless of whether it is an radio frequency (RF) link or an IR link. Being a line-of-sight device, an IR-linked handset must be more carefully thought out and potential problems inherent to a light system as compared to an RF system-must be addressed with particularity in order to have a product which is acceptable to the vast majority of the consumers and users. An IR-linked portable handset in a basic embodiment thereof according to a co-pending application of the assignee of this application filed on even data herewith entitled OPTICAL ANTENNA SYSTEMS FOR INFRARED-LINKED TELEPHONE AND COMMUNICATIONS DEVICES, Ser. No. 07/774,794 by Jerry R. Iggulden et al. is shown in simplified form in FIGS. 4 and 5 where it is generally indicated as 24. The handset 24 comprises a telephone body 26 which can be generally according to prior art IR telephone techniques for purposes of this application since the points of novelty do not reside in those portions of the handset 24. An optical antenna 28 extends upward from the body 26 and has a transmitting/receiving tip 30 on the upper end thereof. The transmitting/receiving tip 30 has a generally hemispherical field of view 32 as indicated by the dashed lines so labelled. FIG. 4 and 5 are not drawn to scale as in a typical handset 24 according to this invention, the radius of the hemisphere would ideally be about one hundred feet.
Other aspects and considerations of an infrared (IR) linked communications system having base station and a portable handset are the battery life of the handset as well as the size and weight of the handset. Cost of manufacture and retail sale to the consumer is also a major factor. In an IR-based wireless public-access telephone system, the cost of the handsets to the consuming and using public should be very low while the cost of the base stations or "telepoints" connected to the telephone lines can be higher. Thus, where performance criteria can be solved in the base station rather than in the handset, it is preferable to do so.
Wherefore, it is an object of the present invention to provide a wireless public access telephone system in which portable, wireless telephone handsets employing IR links to base stations behave like an RF-linked system within line-of-sight and range of the base stations.
It is another object of the present invention to provide a wireless public access telephone system where portable, wireless telephone handsets employing IR links to base stations in which performance criteria are met primarily in the base stations so that the handsets can be low-power, low-cost devices.
It is still another object of the present invention to provide performance enhancements for the base station of wireless public access telephone system where portable, wireless telephone handsets employing IR links to base stations.
Other objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.